The present invention relates to systems for farming aquatic animals in cages and, more particularly, to fish farming systems having a cage which can be submerged and refloated as desired, and to a method for submerging and refloating a fish cage as desired. While specifically referring hereafter to xe2x80x9cfishxe2x80x9d, it is understood that the farming system of the present invention may be used to raise other aquatic animals, e.g. shrimp, oysters, etc.
Considerable efforts have been made in an attempt to supply the rapidly increasing worldwide demand for fish protein. In addition to increasingly sophisticated open sea fishing, a significant fraction of the fish on the market today is raised and harvested using modern aquaculture techniques. Various fish farms have been successfully operating in large man-made pools. However, these farms are expensive to build and operate and do not always make it possible to reproduce optimal conditions for the growth of the fish.
More recently, fish farming has been increasingly carried out in large cages, which are made to float near or at the water surface just offshore (hereinafter xe2x80x9cnear shorexe2x80x9d) in seas, lakes or other natural bodies of water. A fish cage system includes one or more large cages which are typically constructed of a rigid frame of some suitable shape and covered by netting which allows water to flow freely into and out of the cage, but which is of sufficiently fine mesh as to retain the fish inside the cage.
The advantage of such fish cage systems is that they do not take up scarce real estate and do not require the building of an expensive pool. Furthermore, the water conditions (e.g., salinity, temperature, oxygen content, and the like) approximate natural conditions in the open body of water, and may be more optimal for the growth of the fish than conditions simulated in man-made onshore pools.
While the near shore deployment of such fish cages is convenient in terms of accessibility, such deployment suffers from certain disadvantages. As near shore aquaculture develops there is an increasing shortage of quality sites in which to locate additional cages. Many sites suffer from oxygen depletion caused by fish waste and uneaten fish food as well as from industrial, agricultural and domestic runoffs from the nearby shore.
It is therefore often advantageous to avoid onshore locations and to locate the cages farther offshore, in what will be referred to hereafter generically as xe2x80x9cdeep watersxe2x80x9d, i.e. in areas, which are not adversely affected by runoffs and where the greater water circulation serves to dilute fish farm wastes.
However, locating fish cage systems in locations that are remote from the shore poses certain problems. Chief among these is the need to ensure the seaworthiness of the fish cage system in conditions, such as large waves and strong winds during storms, which may be much more severe than those experienced by near shore structures.
Furthermore, it is known that during storms when the water near the water surface is particularly turbulent, fish, which normally spend most of the their time near the water surface where the supply of oxygen is most abundant, tend to temporarily relocate themselves away from the surface to depths where the water is relatively unaffected by the storm and thus avoid damage and stress to themselves.
To minimize or eliminate damage to both the fish and the cages, several fish cage systems have been developed which make it possible to submerge the fish cage to a certain depth when desired, e.g., prior to the onset of a storm, to avoid cold surface water and/or surface ice in winter and hot surface water in summer, or to avoid various toxic contaminants, such as toxic plankton blooms or an oil spill. Zemach et al. in U.S. Pat. No. 5,412,903 which is incorporated herein for all purposes as if fully set henceforth, describe several such previous cage systems, and propose a fish cage system which overcomes some major previous disadvantages and limitations.
FIGS. 1 and 2 depict schematically a prior art fish cage according to Zemach et al. in ""903, in which some of the original details have been omitted. FIG. 1 shows a fish cage 100, typically made of a metal skeleton structure on which is superimposed a netting 102 (shown partially) of suitable mesh size which allows water to flow freely through cage 100 but does not allow fish inside cage 100 to escape. Attached to cage 100 are one or more fish cage cables 104. Cage 100 and cables 104 have combined upward buoyancy imparted through buoyancy chambers or members 106, which ensures that at least, the upper part of cage 100 floats at or above the surface of the water. In cases requiring the temporary lowering of cage 100 to a certain depth, the system is further equipped with a sinker 108 which is connected to cable 104. According to ""903, in a basic embodiment sinker 108 is of fixed and invariable weight which is selected to overcome the combined net buoyancy of cage 100 and cage cables 104 described above, so that when the weight of sinker 108 is added to fish cage 100 and fish cage cables 104 the result is the submersion, preferably at a slow and controlled rate, of cage 100. In another embodiment, sinker 108 is of variable buoyancy, with means provided to increase the buoyancy by introducing air, and to reduce the buoyancy by releasing air, even when sinker 108 is submerged.
Sinker 108 is further connected to a sinker cable 110, which is also connected to a buoy 112 of any suitable design. Buoy 112 is designed to float at the water surface under all conditions. Buoy 112 is equipped with means for alternately shortening and lengthening the effective length of sinker cable 110, means which is preferably a suitable winch mechanism 113 housed within buoy 112, typically one which is operated by an internal combustion engine.
During normal operations, cage 100 is allowed to float at the water surface, as shown in FIG. 1. As described above, the buoyancy of cage 100 (plus fish cage cables 104) is such that cage 100 remains at the water surface. In this condition no external forces are exerted on fish cage cables 104 which stay slack in the water, since sinker 108 to which they are also connected is being fully supported by buoy 112, through sinker cable 110 which is taut (FIG. 1). Buoy 112 is designed to have sufficient buoyancy to support sinker 108 (and sinker cable 110) while still floating at the water surface.
Whenever it desired to submerge cage 100, sinker cable 110 is allowed to lengthen, preferably at a controlled rate, by, for example, releasing a brake mechanism on the winch 113 housed in buoy 112. The weight of sinker 108 then pulls sinker cable 110 out of winch 113, causing it to lengthen as sinker 108 goes deeper. As sinker 108 continues to go deeper there comes a point when fish cage cables 104 become taut, shifting the weight of sinker 108 from sinker cable 110, which becomes slack, to fish cage cables 104 which become taut. Beyond this point, the full weight of sinker 108 is exerted on cage 100. As described above, the incremental weight of sinker 108 is sufficient to overcome the buoyancy of cage 100 and brings about the submersion of cage 100, as shown in FIG. 2 of the prior art.
Preferably, the submersion takes place at a slow rate in order to minimize or eliminate damage to the structures and to the fish. Such a slow rate of submersion can be assured, for example, by carefully selecting the weight of sinker 108 so that the combined weight of the system is just slightly larger than the upwardly directed buoyancy forces. The submersion of cage 100 continues as long as sinker 108 exerts forces on cage 100. As soon as sinker 108 hits bottom these forces are eliminated and cage 100 ceases to move downwardly. Instead, cage 100 stabilizes at a location, which is determined by the length of fish cage cables 104 (FIG. 2).
The system described in ""903 can submerge the cages to virtually any desired depth, provided there is a sufficient length of sinker cable 110. To locate the submerged cage at a certain depth, without regard to the depth of the water, all that is required is the correct length of fish cage cables 104. For example, if it is desired to operated in waters of 200 meters depth and if it is further desired to submerge the cages to a depth of approximately 100 meters, it is required that sinker cable 110 be at least 200 meters long and that fish cage cables 104 be approximately 100 meters long.
Once it is desired to have cage 100 resume its normal position at the water surface, winch 113, or a similar mechanism, is activated to take up sinker cable 110. When sinker cable 110 becomes taut, winch 113 lifts sinker 108 off the bottom and removes its weight from cage 100 whose buoyancy forces now allow it to climb to the surface, preferably at a sufficiently slow rate to avoid structural damage to the system and physiological damage (e.g., the bends) to the fish. Preferably, the lower portions of buoy 112 are shaped to avoid being lifted by cage 100 when cage 100 is raised to the water surface. For example, the lower portions of buoy 112 as shown in FIGS. 1 and 2 are shaped so that as cage 100 is raised to the water surface, cage 100 tends to push buoy 112 away as the upper edge of cage 100 slides up along the ramped lower portions of buoy 112.
Despite the clear advantages it has over prior art systems, the fish cage system of Zemach et al. in ""903 still suffers from a number of problems and disadvantages, some of which are listed below, and which the present invention aims to redress:
One problem arises when cage 100 floats at or near the water surface in weather that is difficult but not stormy enough to warrant submersion of the cage (for example in waves of 0.8-1.8 meter height). In this situation, there are frequent collisions and friction between cage 100, in particular its members 106 and buoy 112. The cage and the buoy have very different floating characteristics on the water, resulting in frequent collisions between them, collisions that cause cumulative damage to both. In emergencies, for example when winch 113 gets stuck and needs to be freed, personnel needs to board buoy 112, and if this action is required in bad weather, it can be life-threatening to the boarding party.
Another problem arises if sinker 108 gets stuck in the muddy or stony sea bottom. This contingency requires buoy 112 to have extra buoyancy (be larger), so that it does not sink itself when it tries to free the stuck sinker. Similarly, winch 113 needs extra pulling capacity for the same reason. These extra requirements make buoy 112 and winch 113 more expensive. Since both the buoy and the winch remain floating in stormy weather while the cage is submerged, damage to either buoy 112 or winch 113, may prevent refloating of the cage.
Yet another problem arises from the fact that the depth to which cage 100 is submerged must be fixed apriori by choosing the length of fish cage cables 104. Once sinker 108 hits bottom, the length of cables 104 cannot be changed, and no further changes in the submersion depth of cage 100 are possible.
An additional problem arises if cage 100, while being submerged, needs to be stopped at some intermediate depth before sinker 108 hits bottom. In this situation, sinker cable 110 may rub frequently against cage 100, in particular against its members 106, so that after a few hours, the friction may rupture cable 110 or slice through a member 106. There is therefore a maximum xe2x80x9cintermediate depth stopover timexe2x80x9d beyond which damage will occur, this time being shortened significantly by bad weather conditions.
A yet additional problem arises with a submerged cage 100 and a floating buoy 112, the latter changing its position according to wind and water current directions. The moving buoy may cause cable 110 to wrap around and get entangled with cables 104 and members 106. An attempt to refloat cage 100 in such a situation may lead to the rupture of cable 110. Attempts to free such an entangled cable 110 require complicated underwater operations using divers.
There is thus a recognized need for, and it would be advantageous to have, a farming system for use in deep waters comprising a fish cage of controlled buoyancy, and a method to submerge and refloat such a fish cage that are devoid of the above problems and limitations.
According to a preferred embodiment of the present invention there is provided a fish farming system, comprising: a fish cage of controllable buoyancy, a winch mechanism attached to the cage, a sinker having a sinker cable of variable length connected to the winch mechanism, an activator mechanism to activate the winch mechanism, the activation thereby defining an effective length of the sinker cable, whereby at least a portion of the fish cage is located at or above the water surface when the buoyancy overcomes the combined force exerted by the weight of the system, and whereby the fish cage is submerged at a desired depth below the water surface when the buoyancy is controllably reduced, the depth being determined by the effective length of the sinker cable.
According to further features in preferred embodiments of the present invention described below, the fish cage includes a plurality of vertical buoyancy elements for imparting the controllable buoyancy.
According to still further features in the described preferred embodiments, the activator mechanism includes a motor capable of receiving wireless instructions, the motor connected to the winch mechanism.
According to still further features in the described preferred embodiments, the activator mechanism further comprises a communication and control conduit functionally connected at one of its ends to the winch mechanism, a remote controller connected to the conduit at its other end, and an auxiliary floating device containing the remote controller, whereby the remote controller and the conduit facilitate activation of the winch mechanism when the winch mechanism is submerged, and the auxiliary floating device prevents the remote controller from being submerged together with the winch mechanism.
According to still further features in the described preferred embodiments, the fish cage includes at least one chamber.
According to still further features in the described preferred embodiments the fish farming system of the present invention further comprises an anchor connected to the fish cage through an anchor cable, and an anchor buoy connected to the anchor cable.
According to still further features in the described preferred embodiments, the anchor buoy comprises a variable buoyancy.
According to still further features in the described preferred embodiments, the system of the present invention further comprises at least one work platform attached to at least one chamber, whereby the winch mechanism is mounted on the platform.
According to still further features in the described preferred embodiments, the system of the present invention further comprises at least one chamber with a cross section lying in a plane substantially parallel to the water surface, which may have a square, round, hexagonal or octagonal shape.
According to still further features in the described preferred embodiments, the system of the present invention further comprises a telemetry device attached to the fish cage.
According to a preferred embodiment of the present invention there is provided a fish farming system, comprising: a fish cage of fixed buoyancy, a winch mechanism attached to the cage, a variable buoyancy sinker having a sinker cable of variable length, the sinker connected to the winch mechanism by the sinker cable, an activator mechanism to activate the winch mechanism, the activator mechanism thereby defining an effective length of the sinker cable, whereby at least a portion of the fish cage is located at or above the water surface when the fixed buoyancy of the cage overcomes the combined force exerted by the weight of the system, and whereby the fish cage is submerged at a desired depth below the water surface when the variable sinker buoyancy is controllably reduced, the depth determined by the effective length of the sinker cable.
According to another embodiment of the present invention there is provided a method of controllably submerging and refloating a fish farming system in deep waters, comprising: providing a fish cage of controllable buoyancy, the fish cage including at least one chamber, attaching a winch mechanism to the cage, connecting a sinker having a sinker cable of variable length to the winch mechanism through the sinker cable, activating the winch mechanism to change the effective length of the sinker cable, and changing the buoyancy of the fish cage, whereby at least a portion of the fish cage floats at or above the water surface when the buoyancy overcomes the combined force exerted by the combined weight of the system, and whereby the fish cage is submerged at a desired depth below the water surface when the buoyancy is controllably reduced, the depth determined by the effective length of the sinker cable.
According to additional features in the described preferred embodiments of the method of the present invention, the activating step includes the use of wireless transmission of instructions.
According to yet additional features in the described preferred embodiments of the method of the present invention, the activating step further comprises functionally connecting a communication and control conduit at one of its ends to the winch mechanism, functionally connecting a remote controller to another end of the conduit, attaching the remote controller to an auxiliary floating device to prevent the remote controller from being submerged, and transmitting control inputs from the remote controller through the conduit to the winch mechanism to activate the winch mechanism.
According to yet additional features in the described preferred embodiments, the method of the present invention further comprises attaching a platform to the cage, and mounting the winch mechanism on the platform.
According to yet additional features in the described preferred embodiments, the method of the present invention further comprises connecting an anchor having an anchor cable to the cage through the anchor cable, and connecting a variable buoyancy buoy to the anchor cable.
According to the present invention there is provided a variable buoyancy buoy, comprising a fixed buoyancy section and a variable buoyancy section attached to the fixed buoyancy section, whereby the buoyancy of the variable buoyancy buoy decreases as the buoy is being submerged.
The present invention successfully addresses the shortcomings of presently known configurations by providing a fish farming system and method for submerging and refloating a fish cage free of prior art limitations.